1. Technical Field
The disclosure generally relates to gas turbine engines.
2. Description of the Related Art
Variable cycle engines power high performance aircraft over a range of operating conditions yet achieve countervailing objectives such as high specific thrust and low fuel consumption. A variable cycle engine essential alters the engine bypass ratio during flight to facilitate efficient performance over a broad range of altitude and flight velocity such as to generate high thrust for maneuver and optimized fuel efficiency for loiter.
Variable cycle engines typically include a variable exhaust nozzle system which operates over a wide range of pressure ratios by adjustment of a nozzle throat based on the demands of the engine cycle, and may include provision for adjustment of a nozzle area ratio to facilitate desired engine performance at various operating points.
The variable cycle engine and exhaust described herein comprises of three flow streams, exhausting through two nozzles. The low pressure compressor stream and core stream exhaust through the primary nozzle. The fan stream exits the variable secondary nozzle. Varying the secondary nozzle alters thrust at the nozzle exit. Also varying the secondary nozzle exit area affects the overall engine cycle by directing of flow into or diverting away from the primary flowpath by varying third stream back pressure, thus effectively altering the bypass ratio.